With respect to a case where a series of videos (live broadcasting videos) are encoded and aired in real time through encoding software such as Window Media Encoder, there are various encoding methods.
Firstly, there is an encoding method, which is direct from a capturing device. Secondly, there is an encoding method, which is indirect from a capturing device.
While the first encoding method has no problem because streaming data already include values corrected errors of A/V from the device, in case of the second encoding method, errors exist during a process of numerically calculating PTS(presentation time stamp) values of A/V based on FPS(frame per second).
For example, 30 FPS means that frames are outputted 30 times per second on a screen, which can be numerically expressed in (1000000000.0 nanosec/30.0)=33333333.333333 . . . and refers to AvgTimePerFrame.
AvgTimePerFrame is significant for determining PTS and refers to a numerical value for determination as to how long videos should be displayed on a screen.
Upon calculating 30 frames per second based on calculated AvgTimeFrame, (33333333*30)=999999990, so that 10 nanosec of an error exists.
Furthermore, in case of a video capturing device, screens of 30 frames are captured corresponding to 30 FPS. However, in case of a personal capturing device such as a webcam, even if 30 FPS per second is set, 30 frames per second are not captured, and less than 30 FPS is captured, so that errors increase. In other words, there is a case where set FPS and the number of FPSs to be captured is inconsistent.
These numerical errors appear to errors between videos and audio during encoding and streaming processes for a long time, thereby causing difficulties in service.
The problem of these errors becomes especially serious in the case where video contents (including video signals and audio signals, and the same meaning applies hereinafter) are processed with different FPSs between a capturing device that generates videos and an encoding apparatus that encodes and transmits the videos.
In case of inserting a video content into another video content, synchronization errors between video signals and audio signals of the respective videos are different. Accordingly, in inserting a video into another video, it may be occurred that videos are played on a screen but sound is off, or sound is on but videos are not played on a screen.
This circumstance causes a problem especially in the case where commercial videos are inserted during public broadcasting. In case of inserting commercial videos during sport broadcasting, if videos are displayed but sound is off, or sound is on but no videos are displayed so that a black screen or others is displayed, viewers may have aversion.